The invention relates to rail cars and more particularly to covered multiple hopper cars of the type used to handle bulk shipments of particulate materials. As a general rule, a covered hopper car can be made in a wide range of sizes to accommodate different volumes of materials. However, in the interest of safety and to prevent overloading of tracks and bridges, limits are also imposed on the gross loading of a rail car and its contents which is applied to the rails. Limits are also imposed on the overall height of its load in order to keep the car's center of gravity within a prescribed limit.
The density of a particular product to be transported by a rail car can vary widely from low density plastic pellets having a density of about 28 pounds per cubic foot, to grain with a density of about 35 pounds per cubic foot and on to aggregate such as sand, gravel and cement having a density of about 90-100 pounds per cubic foot. To maximize load sizing and the efficiencies of handling, it has been common to build cars for specific commodities so that, in the United States, approximately 100 tons of a particular commodity can be transported in a single car. Thus, for example, one might see four-hopper cars used for handling light products, three-hopper cars used for handling grain, and two-hopper cars used for handling cement, sand and gravel. Alternatively, a car can be manufactured which has smaller or larger hoppers, depending upon whether it is being designed to handle a certain weight of a high density material or a low density material. Since a hopper car can have a useful life of 40-50 years, it can and does happen that the existing stock iof all types of hopper cars might periodically be out of balance with the current needs of a nation's economy.
At the present time, there is a considerable oversupply of three-hopper grain hauling cars and an undersupply of two-hopper cars for hauling aggregate. Rather than scraping some of the three-hopper cars and then building new two-hopper cars, it would seem desirable to convert the three-hopper cars to smaller two-hopper cars which would have to be suitable for carrying aggregate.
A method of converting a three-hopper car into a two-hopper car is disclosed in my co-pending U.S. patent application, Ser. No. 828,415, filed Feb. 11, 1986, the subject matter of which is herein incorporated by reference. In the referenced application, the general configuration of the hoppers and their outlet gates is not disclosed as being changed during the conversion. However, when the three-hopper car being converted is a grain carrying car having conventional 24".times.30" outlet gates, the resulting two-hopper car will of course also have 24".times.30" outlet gates. Although such gates can be used to unload cement and aggregate, it is usually necessary to place an adapter onto the receiving structure into which the hoppers are to be unloaded since such receiving structures are generally built to accommodate 13".times.42" outlet gates. The use of adapters and transition seals are especially important when the commodity being carried in the car is cement since cement not only flows like a liquid but can be extremely troublesome if it leaks out or spills during unloading. However, the use of adapters requires additional labor at the receiving location. To eliminate the need for such additional labor, it would be highly desirable to have a 13".times.42" outlet gate permanently installed on a two-hopper car to be used for cement and aggregate service.
Because of the manner in which a hopper car is made, it is not possible to simply substitute a 13".times.42" outlet gate for one that is 24".times.30". This is so since the side slope sheets and the end and center slope sheets of a hopper having a 24".times.30" outlet gate are welded to each other in a special jig or fixture when the hopper car is initially assembled, and the various slope sheets are arranged at particular angles which will direct all of the material in the hopper into the outlet gate. The side slope sheets required for a hopper having a 24".times.30" outlet gate are of course much wider than the side slope sheets required for a hopper having a 13".times.42" outlet gate. Similarly, the end and center slope sheets required for a hopper having a 24".times.30" outlet gate are much more narrow than the corresponding slope sheets required for a 13".times.42" outlet gate. In addition, the most common cement unloading equipment in the U.S.A. is designed for use with dual hopper cars having a center line to center line dimension between hoppers of 12.0 feet. This dimension is 6.375" less than the similar dimension on the converted three-hopper to two-hopper car described in the aforementioned co-pending U.S. patent application Ser. No. 828,415.